<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>ID选择器</title>
<style>
#one{
font-size :20px;
}
#two{
font-size :11px;
}
#three{
font-size :34px;
}
</style>
</head>
<body>
<p id = "one">ID选择器</p>
<p id = "two">ID选择器</p>
<p id = "three">ID选择器</p>

</body>
</html>